Print-use download options: These files are designed to fit on letter-size paper

ABOUT THIS IMAGE:

Like dust bunnies that lurk in corners and under beds, surprisingly
complex loops and blobs of cosmic dust lie hidden in the giant
elliptical galaxy NGC 1316. This image made from data obtained
with the NASA Hubble Space Telescope reveals the dust
lanes and star clusters of this giant galaxy that give evidence
that it was formed from a past merger of two gas-rich galaxies.

The combination of Hubble's superb spatial resolution and the
sensitivity of the Advanced Camera for Surveys (ACS), installed
onboard Hubble in 2002 and used for these images, enabled uniquely
accurate measurements of a class of red star clusters in NGC 1316.
Astronomers conclude that these star clusters constitute clear
evidence of the occurrence of a major collision of two spiral
galaxies that merged together a few billion years ago to shape NGC
1316 as it appears today.

NGC 1316 is on the outskirts of a nearby cluster of galaxies in the
southern constellation of Fornax, at a distance of about 75 million
light-years. It is one of the brightest ellipticals in the Fornax
galaxy cluster. NGC 1316, also known as Fornax A, is one of the
strongest and largest radio sources in the sky, with radio lobes
extending over several degrees of sky (well off the Hubble image).

NGC 1316's violent history is evident in various ways. Wide-field
imagery from Cerro Tololo Interamerican Observatory in Chile shows
a bewildering variety of ripples, loops and plumes immersed in the
galaxy's outer envelope. Amongst these so-called "tidal" features, the
narrow ones are believed to be the stellar remains of other spiral
galaxies that merged with NGC 1316 some time during the last few
billion years. The inner regions of the galaxy shown in the Hubble
image reveal a complicated system of dust lanes and patches. These are
thought to be the remains of the interstellar medium associated with
one or more of the spiral galaxies swallowed by NGC 1316.

The U.S. team of scientists, led by Dr. Paul Goudfrooij of the Space
Telescope Science Institute in Baltimore, Maryland, used the ACS
onboard Hubble to study star clusters in several nearby giant
elliptical galaxies. Their study of NGC 1316 focused on globular
clusters, which are compact stellar systems with hundreds of
thousands to millions of stars formed at the same time.

The unprecedented sensitivity of the Hubble ACS data permitted the
team to detect faint globular clusters previously impossible to
reach. By counting the number of globular clusters detected as a
function of their brightness they could, for the first time, see
evidence of the gradual disruption of star clusters created during
a past merger of gas-rich galaxies. They found that the relative
number of low-mass clusters is significantly lower in the inner
regions than in the outer regions, by an amount consistent with
theoretical predictions.

These Hubble ACS images were taken in March 2003. The color composite
is a combination of data taken in F435W (blue), F555W (yellow-green),
and F814W (infrared) filters.
The team's results have improved our understanding of how elliptical
galaxies and their star clusters may have formed during galaxy mergers
and then evolve to resemble 'normal' elliptical galaxies after several
billions of years.